I'm not sure about that... from Jan 2014 to now is just under 2 full years if your status is still single, that you will need to correct for.
Yes to be right with the CRA and prevent hardship in case you are ever audited in the future, you should do a re-assessment of your 2014 taxes. You've already acknowledged that there may be some payments you will need to give back to the government, but also note that if one of you had minimal income in 2014 then the other can claim them under the spousal tax credit and possibly get some additional money back for 2014 tax year. Impossible to say what will happen in your case without getting into income details.
However the CRA issue and your CIC PR app are 2 different things. I wouldn't let the CRA re-assessment and time that will take, stop you from completing and submitting your PR app. I don't think CIC will care if your option C says single or common-law, and if asked you can indicate you're doing a re-assessment of the 2014 tax year. In terms of Option C, CIC is more looking for your financial information. So I would just submit based on what you have now even before you have the 2014 re-assessment completely done.